Five innovations that boost soil fertility

Farmers and scientists are going beyond the massive use of chemical fertilizers to find innovative methods to improve soils and yields.

Barry Malone/Reuters/File

A farmer threshes maize (corn) in Abay, north of Addis Ababa, Ethiopia. Techniques from applying "green manure" to "microdoses" of fertilizer are being tried to improve degraded soils around the world and boost agricultural output.

Crops need air, sun, water, and soil to thrive. When it comes to soil, however, quality usually trumps quantity. Rich and fertile land boasts a healthy mixture of phosphorous, potassium, and nitrogen, along with water, air, and soil micro-organisms that break down organic matter.

But what happens when these elemental building blocks are disrupted? The Green Revolution of the mid-20th
century implemented a variety of practices, including the widespread use of pesticides and fertilizers. Yet, improperly applying the Green Revolution’s principles can sometimes do more harm than good.

Overfertilizing and destructive land use practices, including deforestation, can deplete vital nutrients in soil, and no amount of inorganic fertilizer can replace fundamental topsoil. In addition, higher annual temperatures, more extreme weather events and persistent droughts, and increasing population are also exhausting the land. These conditions are creating a cycle of soil degeneration which is stunting agricultural yields and presenting farmers with a new crop of concerns.

Today, Nourishing the Planet provides five methods that farmers and scientists are using to combat rising soil infertility.

1. Cover Cropping / Green Manure: In our State of the World 2011 report, agroecologist and author Roland Bunch defines cover crops / green manure as “any plant, whether a tree, bush, or vine, that is used by a farmer to … improve soil fertility or control weeds.” In practice, cover crops are planted alongside or interspersed with other crops to cut soil-eroding wind, prevent overexposure to the sun, and stimulate a healthy soil system. Just as farmers will turn to manure to bolster the soil, they can also clip and spread cover crops’ leaves as organic green manure.

Cover Cropping / Green Manure in Action: According to Roland Bunch, there are more than a million farmers now actively using cover crops / green manure worldwide. In Africa alone, there are over 120 plant species that are being used or could be used for this purpose. One promising example is the cowpea (also known as the black-eyed pea). This legume is both a nitrogen-fixer, which means that it takes nitrogen from the air and replenishes it in the soil, and deeply rooted, which makes it resistant to drought. Furthermore, the cowpea itself is a nutritious staple food for both people and animals.

2. Microdosing Fertilizer: According to the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), microdosing is defined as “the application of small, affordable quantities of fertilizer with the seed at planting time or as top dressing 3 to 4 weeks after emergence.” This precise process stands in stark contrast with the field-wide fertilization used by many farmers. Fertilizers are often very expensive for farmers in the developing world, particularly in sub-Saharan Africa. Microdosing can help reduce fertilizer costs, while also targeting the seeds farmers want to cultivate.

Microdosing in Action: ICRISAT has initiated microdosing programs in Mali, Burkina Faso, and Niger, reaching over 25,000 small-holder farmers. The Institute reports that sorghum and millet yields have responded well to the technique – boosting yields between 44 and 120 percent – and that incomes have also increased by as much as 130 percent for some families. ICRISAT is working with agricultural extension services to better instruct farmers on how to effectively measure and apply fertilizer. The Institute has also lobbied private fertilizer companies to distribute their product in premeasured and prepackaged microdoses.

3. Using Wastewater for Irrigation: As urban areas grow in developing countries, residents and governments are struggling to find ways to properly dispose of sewage and waste water. The United Nations Food and Agriculture Organizationnotes that wastewater contains most of the essential elements of fertilizer in the proper amounts. Effective treatment and application of wastewater could dually contribute to healthier urban areas and provide vital, organic fertilizer to rural areas.

Wastewater Irrigation in Action: Using effluent wastewater as an agricultural fertilizer could be an easy way for farmers, especially in cities, to fertilize their crops; but it can be risky. As Pay Drechsel wrote in State of the World 2011, “In Ghana and surrounding areas, polluted stream water is often used to irrigate vegetable crops. The problem is that the water often contains biological and chemical substances that are harmful to human health.” The Bill and Melinda Gates Foundation, however, recently announced a program that may make this a more practical option for farmers. The foundation will be spending $42 million in sanitation grants over the next few years to “reinvent the toilet.” The hope is that this money will help build better human waste infrastructure in urban areas, promote improved sanitation, and effectively capture the wastewater for use in energy and fertilizer.

4. Reintegrating Livestock: As many as 1 billion people around the world “rely on farm animals for their livelihoods,” according to researchers from the International Livestock Research Institute. But animals are not only important for their egg and meat production, but also because they can be integrated into larger agricultural systems. Animal manure can be an effective – and inexpensive – way to boost the health of organic topsoil.

Livestock Integration in Action: International organizations are beginning to recognize the potential and value of these integrated farming systems. The African Wildlife Foundation’s Heartland program and the multinational TerrAfrica project are both promoting sustainable land and water management practices in drought-prone areas of the continent. In Botswana, the Mokolodi Nature Reserve is both a wildlife preserve and an educational center, sending staff to teach local farmers sustainable ecoagriculture and integrated livestock farming techniques.

5. Preventing Nitrogen Leaching (Inhibitors): Nitrogen is essential to healthy soil. Chemical fertilizers and nitrogen-fixing plants, such as legumes, can help provide nitrogen to soils. Yet, nitrogen, like water, follows a cycle that includes leaching or escaping from the ground as a gas. Poor land management, erosion, overfertilization, and chemical runoff can all contribute to nitrogen depletion, which will leave the land dry and unusable. To combat nitrogen loss, soil scientists have been experimenting with chemical inhibitors that will keep vital nutrients in the ground longer.

Inhibitors in Action: Studies show that chemical inhibitors do actively stimulate the nitrogen cycle, keep more nitrogen in the soil for longer periods, and may increase crop yields. Dr. Bob Hoeft at the University of Illinois recorded 15-20 bushel / acre increases after using chemical inhibitors. Internationally, tests in Brazil found a marked increase in sugarcane production after applying the chemical nitrogen-fixers. These inhibitors are not the absolute solution to nitrogen depletion, but if they are used in small doses properly with natural nitrogen-fixers and better land management, they can rebuild healthy soil into the future.

• Joseph Zaleski is a research intern with the Nourishing the Planet project.